The present invention relates to a rock drill bit of the impact type comprising a mainly cylindrical body and a front surface, provided with a number of fixed peripherally spaced inserts, each said insert having a body with a generally cylindrical jacket surface and a head section protruding axially outwardly from the front surface.
Rock drill bits of the above-captioned type have inserts with semi-spherical head sections. A drawback of this shaping is that the semi-sphere is being worn to a conical configuration at the part of the working end which is turned away from the centre axis of the rock drill bit. The conical configuration adversely affects the boring rate so that the necessary feed force will increase and so that the rock drill bit tends to follow cracks in the rock material. The rock drill bit will thus be guided in a negative manner so that the bore gets inclined in the longitudinal direction and therefore a regrinding of the inserts will be necessitated after only a short period of drilling. Also in the beginning of the drilling there is a need for a large feed force because the semi-spherical shape itself to a certain degree contains a conical configuration.
The object of the present invention is to provide an improved rock drill bit in which the inserts have a configuration that makes it possible to drill with a constant boring rate during long drilling intervals without resistance from any conical configuration and without regrinding of the head section of each insert.